Marine fouling is a major problem in the transport of materials by sea as it can raise fuel consumption by as much as 30%. Environmentally friendly coatings that protect the hulls of ships below the waterline against fouling by seaweed, barnacles, and other organisms are currently sought by the shipping industry. Fouling by these organisms produces additional drag on the ship, thereby increasing operating and maintenance costs.
Antifouling paints containing tin and copper biocides are currently used because of their effectiveness against most forms of marine fouling. Many of these biocidal organometallic compounds are environmentally persistent. They can cause damage to the ecosystem and enter the food chain. The ban on tributyltin (TBT) antifoulants by the International Maritime Organization will be effective in 2008, and copper-based coatings are expected to face similar restrictions in the near future.
Non-toxic “fouling-release” or “fouling-repellant” coatings are one class of alternatives to biocidal coatings. Silicone-based paints are commercially available, but do not satisfy many desired performance characteristics. The soft silicones do not withstand the rigorous demands of the marine environment, do not sufficiently and consistently self-clean, or, due to polymer restructuring or other degradation pathways, lose many of the desirable surface properties with time and exposure to marine organisms.
Several fouling release (FR) coating systems are commercially available, mostly based on silicone polymers, yet none meet all of the desired performance characteristics. Many commercially available coating systems lack the toughness required to withstand the rigorous physical demands of the marine environment, do not sufficiently and consistently self-clean, and due to polymer restructuring or other degradation pathways, lose many of the desirable surface properties with time and exposure to the marine environment.
Current understanding of antifouling materials is that the most effective copper-free fouling control systems are low surface energy coatings, namely silicone or fluoropolymer based coatings that minimize the adhesion strength between fouling organisms and surface. For extended performance life, these coating systems should have controlled and stable surface energy, elastomeric properties, and should adhere well to the substrate.
What is needed is a material that has antimicrobial properties to reduce marine biofouling, thereby decreasing the accumulation and buildup of marine organisms and aiding in their removal. Such a material would preferably lack toxic copper or tin metals, and lower the strength of adhesion between marine fouling organisms and surfaces in contact with a marine environment. The diversity of fouling organisms and environmental conditions worldwide makes the task of developing a coating that resists fouling and/or self-cleans challenging, and novel solutions to the problem are urgently needed.